Pressurized fluid systems are provided with pressure relief capabilities to prevent injury to personnel and damage to equipment. In the event of an overpressure condition, a pressure relief valve redirects the fluid flow to a bypass path or to a shut-off path. Pressure relief valves are usually configured to be either normally open or normally closed to fluid passage. Exemplary pressure relief valve assemblies are taught by U.S. Pat. No. 7,438,087 issued to Taylor.
Some types of pressure relief valves use a spring loaded valve member that is urged against a valve seat and configured to permit the pressurized fluid to contactingly engage the normally closed valve member. The spring maintains the valve member in the closed position, while the fluid pressure opposes the spring force to urge the valve member to the open position.
If the valve is operated at a working fluid pressure that is relatively close to the pressure setpoint, which is the pressure at which the valve will open to establish a bypass path, the net force applied to the valve member by the spring may be insufficient to maintain a bubble-tight seal. The valve will thus simmer, permitting small amounts of pressurized fluid to escape through the assembly. Depending on the nature of the pressurized fluid, this can result in a number of undesired effects including environmental contamination (pollution), loss of product volume and hazards to personnel and/or downstream equipment.
One way in which prior art solutions have endeavored to reduce the effects of simmering is to remove the valve member from the inlet fluid pressure through the use of an upstream rupture disk. The rupture disk generally serves as a membrane to isolate the downstream valve from normal fluid pressure. The rupture disk is intended to retain the fluid until the overpressure condition is reached, upon which the disk ruptures and the pressurized fluid passes to the pressure relief valve member. In such case, the fluid pressure is sufficient to overcome the spring bias force on the valve member, moving the valve member to the open position for fluid passage to a bypass path.
A limitation with this approach includes the fact that any fluid pressure that may develop between the upstream and downstream devices, such as via a leak through or around the rupture disk, will generally tend to alter the differential pressure across the upstream device. In such case, the set point at which the upstream device opens will be undesirably higher than the specified level.
It is thus common to use pressure indicators to detect such buildup of pressure between the upstream and downstream devices. When an undesirably high level of intermediate pressure is detected, maintenance action is required to address the situation, which can include replacing the upstream rupture disk, involving substantial effort and downtime to access and replace the failed rupture disk.
Another limitation associated with the use of rupture disks is the fact that while rupture disks are generally intended to open in a controlled manner and remain in a single piece, the disks can separate upon rupturing and fragments can be carried by the fluid flow to the main pressure relief valve. This is undesirable as such fragments can interfere with the proper opening and subsequent closing of the main valve.
There continues to be a need for improvements in the manner in which overpressure conditions in pressurized fluid system configurations can be detected and relieved. It is to these and other improvements that various embodiments of the present invention are generally directed.